Package com.smartgwt.client.widgets.form.fields.events

# Interface ChangeHandler

All Superinterfaces:
  `EventHandler`

public interface ChangeHandler extends EventHandler

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `onChange(ChangeEvent event)`
  Called when a FormItem's value is about to change as the result of user interaction.

- ## Method Details

  - ### onChange

    void onChange(ChangeEvent event)
    Called when a FormItem's value is about to change as the result of user interaction. This method fires after the user performed an action that would change the value of this field, but before the element itself is changed.

    Returning false cancels the change. Note that if what you want to do is transform the user's input, for example, automatically change separator characters to a standard separator character, you should implement `transformInput` rather than using a combination of change() and setValue() to accomplish the same thing. Returning false from `change` is intended for rejecting input entirely, such as typing invalid characters.

    Note that if you ask the form for the current value in this handler, you will get the old value because the change has not yet been committed. The new value is available as a parameter to this method.

    Change/Changed notifications vs "...When" rules: the `change` and `changed` events only fire when an end user modifies a field value. If you are trying to dynamically control the visibility or enabled state of other components in response to these events, consider instead using properties such as `Canvas.visibleWhen`, `item.readOnlyWhen`, `Canvas.enableWhen` on the target component. (Similar properties are available on `FormItem`, `Canvas`, `MenuItem` and other components).

    Parameters:
      `event` - the event